Arrangement in a pulp grinder

ABSTRACT

An arrangement in a pulp grinder comprising a grindstone ( 1 ), a feed chute ( 2 ), and a piston to feed wood ( 3 ) against the grindstone ( 1 ). The arrangement comprises separate pushing members ( 6 ), which are arranged to push the wood ( 3 ) against the grindstone ( 1 ) at essentially the entire width of the feed chute when the percussion piston is moved back to the stroke position to allow the feed of a new batch of wood.

The invention relates to an arrangement in a pulp grinder comprising agrindstone, a feed chute extending to the grindstone, and a piston tofeed the wood to be ground in the feed chute against the grindstone, thewood being fed into a grinding space essentially in the axial directionof the grindstone.

When wood is ground to produce fibres, the grinders typically used aregrinders in which the blocks of wood are pressed against the surface ofa rotary grindstone, simultaneously spraying water there to produce apulp suspension. The most generally, the wood supply is implemented inpulp grinders on a discontinuous basis: one batch of wood at a time isfed into a feed chute, after which the wood in the feed chute is pressedby a cylinder and a piston against the grindstone. In order that theoutput would be as great as possible, two feed chutes, with cylinders,are usually arranged on the opposite sides of the grindstone.Consequently, when a feed chute is being filled, the grindstone issubjected to less load than when both the feed chutes are in thegrinding step, and this causes both uneven loading and variation in thequality of the ground pulp. Further, the drawback of the discontinuoussupply is that the output is smaller when the wood is fed in batchesthan when continuous grinding is used. Another problem in thediscontinuous grinding is that the blocks of wood fed during thecompression press more firmly against each other, which also results invariation between the production rates at the beginning and at the endof the grinding. Consequently, for example the freeness of the groundpulp is higher at the beginning of the compression, dropping toward theend of the furnace, even if the feed rate at the piston of the cylinderis adjusted to remain constant. For the same reason, the motor is loadedunevenly.

Previously known are also continuous grinders in which the continuouswood supply is based on moving feed chains on both sides of a feed chuteand on the weight of the wood in the feed chute. Such a grinder isknown, for example, from German Offenlegungsschrift 2,8 12,299. Thedrawback of the solution is that to provide the continuous wood supplyand sufficient compression, the chains must be rather long, which inpractice means that the feed chute must be up to 6-8 meters high. Thecontact surface between the chains and the blocks of wood that are beingfed is thus sufficiently large, and the weight of the pile of woodsimultaneously helps to press the wood against the feed chains forcompression. Because of this, only an essentially upright feed chute canbe used in the grinding process, which notably restricts the amount ofwood that can be ground simultaneously. As a result, the capacity of thegrinder is naturally smaller than in solutions where wood fed from twoor more feed chutes can be ground simultaneously. Another problem in thehigh feed chute is that the blocks of wood may settle obliquely, whichaffects the grindstone and because of which the grinder must besharpened unduly often in order to correct the obliqueness. Since thepressing force of the chains does not divide evenly between the blocksof wood in the feed chute, but in practice the blocks of wood that arethe closest to the chains are fed at a higher feed rate than those inthe middle of the feed chute, this affects the quality and may alsocause the above obliqueness.

The object of the present invention is to provide an arrangement in agrinder in which wood can be fed continuously in an essentiallyunchanged manner against the grindstone, maintaining the grindingconditions essentially unchanged, and feeding the wood into the grinderin batches. The arrangement of the invention is characterized in thatthe arrangement comprises pushing members on two opposite sides of thefeed chute, the pushing members being insertable at the end of thepiston's travel distance into recesses in the piston crosswise of thefeed chute behind the wood to be ground and being able to push the woodto be ground toward the grindstone when the piston is moved to thebeginning of its travel distance so as to allow the feed of a new batchof wood.

The essential idea of the invention is that it comprises separatepushing members which at the end of the piston stroke push through theapertures formed in the piston to press the batch of wood toward thegrindstone at essentially the entire width of the feed chute in thecrosswise direction so that the piston can move to the starting positionof its stroke to allow the feed of a new batch of wood, and that whenthe piston pushes the new batch of wood toward the grindstone, thepushing members move aside so as to allow the new batch of wood to pressthe wood already in the feed chute.

The invention will be described in greater detail with reference to theattached drawings, in which

FIGS. 1a to 1 e illustrate an embodiment of the arrangement according tothe invention shown as a sectional side view of the feed chute,

FIG. 2 is a schematic view of another embodiment of the arrangementaccording to the invention shown as a sectional side view of the feedchute, and

FIG. 3 is a schematic top view of a piston suitable for use in theembodiments of the invention illustrated in FIGS. 1 and 2.

FIGS. 1a to 1 e show a partial view of a grinder comprising a grindstone1 that rotates about its axle. Further, the grinder comprises a feedchute 2 in which there is wood 3 that is pushed by a piston, connectedto a feed cylinder 4, toward the grindstone 1. The figures also showpushing members 6. The pushing members 6 move lengthwise of the feedchute 2 and comprise pushing heads 6 a extending to the feed chute 2 sothat when the pushing heads 6 a are in the feed chute 2, they togetherextend at essentially the entire width of the feed chute 2. The pushingmembers 6 are connected with articulations 6 b to pushing cylinders 7,by which the pushing members 6 can be moved lengthwise of the feed chute2. In this embodiment the pushing members 6 are arranged to be guided byguide rails 8, and the guide rails 8, in turn can be moved by guidecylinders 9 either toward the feed chute 2 or away from it, depending onthe situation. As shown by the sectional view of FIG. 1a, the piston 5comprises a recess into which the pushing head 6 a can push behind thewood 3 when the piston 5 presses the wood 3 toward the grindstone 1 uponending the stroke.

The arrangement according to the invention operates so that when wood isground, the piston 5 pushes the wood 3 in the feed chute 2 toward thegrindstone 1, until the piston 5 reaches the position shown in FIG. 1a.The pushing members 6 are here at their extreme position, the furthestaway from the grindstone 1, and they can be pushed by the guidecylinders 9 and the guide rails 8 into the recesses in the piston 5inside the feed chute 2. The wood 3 is then pushed further toward thegrindstone 1 by the pushing cylinders 7 that act on the pushing heads 6a of the pushing members 6, whereby the guide rails 8 guide the pushingmembers so that the pushing heads 6 a stay inside the feed chute 2,compressing the wood 3. The piston 5 is simultaneously pulled by thefeed cylinder 4 to the rearmost position of its travel distance, shownin FIG. 1b, and a new batch of wood 3′ is fed in front of the piston 5on the side of the grindstone 1 by pushing the wood into the feed chute2 in the axial direction of the grindstone 1. This can be effected in amanner known per se, for example according to the embodiments describedin Finnish Patent 69,653 or some other previously known embodiments.After this, the piston 5 is moved by the feed cylinder 4 toward thegrindstone, whereby it presses the new batch of wood 3′ against thatsurface of the pushing heads 6 a of the pushing members 6 which is onthe side of the piston. The batch of wood '3 is thus compressedsimultaneously as the pushing members and the pushing heads press thewood 3 that has been supplied earlier toward the grindstone.

When the new batch of wood 3′ has been compressed sufficiently tightly,the pushing heads 6 a of the pushing members 6 are slowly pulled outwardof the feed chute 2 so that the new batch of wood 3′ is pressed by thepiston 5 against the wood 3 that has been supplied earlier, and the feedof the wood will continue in this way continuously and evenly, while thecompression remains essentially unchanged. When the pushing heads 6 a ofthe pushing members 6 have been pulled out of the feed chute, thepushing members 6 are moved back to their initial position by thepushing cylinders 7, while the piston 5 continues to press the wood 3against the grindstone 1. When the pushing members 6 are again in theirextreme position the furthest away from the grindstone 1, and when thepiston 5 approaches the end of its stroke, the pushing heads 6 a areagain pushed into the recesses of the piston 5 in the feed chute by theguide rails 8 and the guide cylinders 9 in the manner shown in FIG. 1a,and the cycle of operation will be repeated.

The advantage of the arrangement is that wood can be supplied to thegrinder in batches, which is the simplest and the most reliable feedingmethod up to a point. Simultaneously, the compression that the wood issubjected to and thereby the conditions between the wood and thegrinding surface of the grindstone are maintained essentially constant,since separate pushing members are used. Consequently, the supply ofwood against the grindstone is thus essentially continuous and happensessentially evenly, whereby an essentially even continuous grindingprocess is provided, in which the characteristics of the ground pulpvary essentially less than before, and the loading of the motor of thegrinder can be maintained essentially constant and advantageous inrespect of the grinding.

FIG. 2 illustrates another embodiment of the arrangement according tothe invention, showing a sectional side view of the feed chute. In theembodiment of FIG. 2, each pushing member 6 consists of two pushingheads 6 a, which join to form a member rotating about an axle 10.Pushing members like this are arranged on both sides of the feed chute2, and when they are essentially crosswise of the feed chute 2, theyextend at essentially the entire width of the feed chute in thecrosswise direction. Even in this embodiment the piston comprisesrecesses corresponding with the pushing members 6 so that the pushingheads 6 a of the pushing members 6 can turn inside the piston 5 when thepiston is essentially in the pressing position. In this embodiment, thepushing members rotate, and as they rotate they press the wood 3 in thefeed chute 2 toward the grindstone 1 while the piston 5 moves away fromthe grindstone so as to allow the feed of a new batch of wood.Correspondingly, when the new batch of wood 3′ is compressed in front ofthe piston 5 toward the grindstone, the pushing heads 6 a turn outwardof the feed chute, thereby allowing the new batch of wood 3′ to pressagainst the wood 3 that has been supplied to the feed chute earlier, sothat in the end all the wood is pressed only by the piston 5. Tosimplify the operation, the pushing members 6 turn about the axles 10 intwo phases so that the pushing members 6 turn one full round per twopiston strokes. The surfaces of the pushing members 6 are such that whenthe pushing members are in the feed chute 2, their surface toward thegrindstone 1 is curved, whereby they can be moved more easily along thewood to be pressed outward of the feed chute.

FIG. 3 shows, by way of example, a top view of a piston 5 suitable foruse in the implementation of the solution according to FIGS. 1a to 1 eand FIG. 2. FIG. 3 shows that the piston 5 comprises two recesses 5 a,in which the pushing members 6 can settle when the piston 5 is pressedagainst the wood 3. There may be one or more such recesses 5 a,depending on how many and what kind of pushing members are used aboveand below the feed chute 2.

The essential feature is that the compression effected by the pushingmembers is symmetrical so that the wood stays compressed against thegrindstone 1 at the entire width of the feed chute 2, whereby thefeeding and grinding processes are even.

The above description and the drawings present the invention only by wayof example, without limiting it in any way. The essential feature of theinvention is that in addition to the pressing piston it comprisesseparate pushing members, by which the wood can be pushed furtheragainst the grindstone when the percussion piston ends the stroke andmoves back to the initial position so as to allow the feed of a newbatch of wood. Another essential feature is that at some point of thestroke of the percussion piston the pushing members 6 are pulledessentially entirely out of the feed chute so that the percussion pistoncan compress the wood in the feed chute tightly before the feed of a newbatch of wood. In the embodiments of FIGS. 1a to 1 e and of FIG. 2, thepushing members 6 are preferably symmetrically on the opposite sides ofthe feed chute 2. Further, they can comprise one pushing head or thelike on both sides in the middle of the feed chute, or two or morepushing heads and potentially also pushing members on one and the sameside of the feed chute. Correspondingly, the piston 5 then comprises acorresponding number of recesses, so that each pushing head can pushinto the piston behind the wood. In the embodiment illustrated by thefigures, the pushing members 6 are arranged on those sides of the feedchute 2 which are parallel to the axle of the grindstone 1. Since thewood 3 in the feed chute is also parallel to the axle of the grindstone1, the pushing members can be pushed behind the wood crosswise thereof.Also, the surfaces of the piston 5 that come into contact with the woodare also crosswise of the wood, which enables the implementation of theprocess in accordance with the invention. The invention is notrestricted to a pulp grinder of a certain type. It can thus be used inboth non-pressure grinders and pressure grinders, the other necessaryoperations and apparatuses being implemented conventionally in apreviously known manner so that they are suited to the solutions inquestion.

What is claimed is:
 1. An apparatus for grinding wood in a pulp grinder,the apparatus comprising: a grindstone; a feed chute extending to thegrindstone for feeding wood therein to the grindstone along a feeddirection, the feed chute defining a width crosswise to the feeddirection; a piston movable within the feed chute along the feeddirection for pressing wood in the feed chute against the grindstone,the piston being retractable away from the grindstone to allow a newbatch of wood to be fed into the feed chute ahead of an end of thepiston that presses against the wood, the end of the piston definingrecesses therein; and pushing members disposed on two opposite sides ofthe feed chute, the pushing members being insertable into the recessesin the end of the piston when the piston reaches an end of its travel inthe feed direction such that the pushing members move behind the wood inthe feed chute, the pushing members being structured and arranged topush the wood in the feed direction toward the grindstone as the pistonis retracted to allow a new batch of wood to be fed into the feed chute.2. The apparatus of claim 1, wherein the pushing members comprisepushing heads that together extend across substantially the entire widthof the feed chute.
 3. The apparatus of claim 1, wherein the pushingmembers comprise pushing heads connected to pushing cylinders operableto move the pushing heads lengthwise of the feed chute, the pushingheads further being movable crosswise of the feed chute for moving intothe feed chute behind the wood and for moving back out of the feed chuteafter a new batch of wood is fed into the feed chute and the pistonbegins pressing the new batch toward the grindstone.
 4. The apparatus ofclaim 3, further comprising guide rails on the two opposite sides of thefeed chute, the guide rails being movable crosswise of the feed chutetoward and away therefrom by guide cylinders connected to the guiderails, and the pushing heads being connected to the guide rails formovement therewith in the crosswise direction.
 5. The apparatus of claim1, wherein the pushing members comprise pushing heads rotatable aboutaxles so that rotation of the pushing heads causes the pushing heads tomove into the recesses in the piston and into the feed chute behind thewood, and further rotation of the pushing heads causes the pushing headsto press the wood toward the grindstone.
 6. The apparatus of claim 1,wherein the pushing members comprise pushing heads, and the pushingmembers are movable such that in at least one position of the pushingmembers the pushing heads are essentially entirely outside the feedchute.
 7. The apparatus of claim 1, wherein the pushing members arearranged on sides of the feed chute that extend parallel to an axle ofthe grindstone.